A lightguide pulse transmission system uses wideband repeaters for regenerating signals to overcome pulse attenuation that occurs in the lightguide. Because system signal levels vary as a result of component age and ambient temperature changes, it is helpful to use automatic gain control in the repeaters. The operating frequency of the lightguide system is so high that designing a linear amplifier with automatic gain control presents many problems. One problem is the design of a controllable integrated circuit with a smooth characteristic over a very wide frequency range.